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NCCIH Clinical Digest

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NCCAM's 5 Most Searched-For Herbs of 2012:
What the Science Says

January 2013

The following are the top five searched-for herbs that led visitors to the NCCAM Web site.

1. Evening Primrose Oil

Evening primrose oil is a plant native to North America and has been used as a folk or traditional remedy for eczema, rheumatoid arthritis, and menopausal symptoms. Evening primrose oil contains gamma-linolenic acid (GLA), an essential fatty acid.

Strength of Evidence

  • Overall, only a few small exploratory studies of evening primrose oil have been published. The evidence is insufficient to draw clear conclusions about efficacy.

Study Results

  • Results from these studies suggest hints of modest benefits for eczema, rheumatoid arthritis, breast pain, and premenstrual syndrome.
  • Evening primrose oil does not appear to affect menopausal symptoms.
  • There is not enough evidence to support the use of evening primrose oil for other health conditions.

Side Effects and Cautions

  • Evening primrose oil appears to be well tolerated by most people. Side effects include mild gastrointestinal upset and headache.

2. St. John’s Wort

Historically, St. John’s wort has been used for centuries to treat mental disorders and nerve pain. St. John’s wort has also been used for malaria, as a sedative, and as a balm for wounds, burns, and insect bites. Today, St. John’s wort is used as a folk or traditional remedy for depression, anxiety, and/or sleep disorders.

Strength of Evidence

  • St. John’s wort has been studied extensively for depressive disorders in both the United States and Europe, and for its interactions with a number of drugs.

Study Results

  • A 2009 systematic review of 29 international studies suggested that St. John’s wort may be better than a placebo and as effective as standard prescription antidepressants for major depression of mild to moderate severity. St. John’s wort also appeared to have fewer side effects than standard antidepressants. The studies conducted in German-speaking countries—where St. John’s wort has a long history of use by medical professionals—reported more positive results than those done in other countries, including the United States.
  • Two large studies sponsored by NCCAM and the National Institute of Mental Health did not show benefit. Neither St. John’s wort nor a standard antidepressant medication decreased symptoms of minor depression better than a placebo in a 2011 study. The herb was no more effective than placebo in treating major depression of moderate severity in a 2002 study.
  • Basic research studies suggest that St. John’s wort may prevent nerve cells in the brain from reabsorbing certain chemical messengers, including dopamine and serotonin. These naturally occurring neurotransmitters are known to be involved in regulating mood, but much remains to be learned about exactly how they work.

Side Effects and Cautions

  • Research has shown that St. John’s wort interacts with many medications in ways that can interfere with their intended effects. Examples of medications that can be affected include:
    • Antidepressants
    • Birth control pills
    • Cyclosporine, which prevents the body from rejecting transplanted organs
    • Digoxin, a heart medication
    • Indinavir and possibly other drugs used to control HIV infection
    • Irinotecan and possibly other drugs used to treat cancer
    • Seizure-control drugs, such as phenytoin and phenobarbital
    • Warfarin and related anticoagulants.
  • St. John’s wort may cause increased sensitivity to sunlight. Other side effects can include anxiety, dry mouth, dizziness, gastrointestinal symptoms, fatigue, headache, or sexual dysfunction.
  • Taking St. John’s wort with certain antidepressants may lead to increased serotonin-related side effects, which may be potentially serious.
  • St. John’s wort is not a proven therapy for depression. If depression is not adequately treated, it can become severe. Anyone who may have depression should see a health care provider. There are effective proven therapies available.

3. Fenugreek

Historically, fenugreek was used for a variety of health conditions, including menopausal symptoms and digestive problems. It was also used for inducing childbirth. Today, fenugreek is used as a folk or traditional remedy for diabetes and loss of appetite, and to stimulate milk production in breastfeeding women. It is also applied to the skin for inflammation.

Strength of Evidence

  • Only a few small studies have examined fenugreek for any health condition.

Study Results

  • While results suggest that fenugreek may help lower blood sugar levels in people with non-insulin dependent diabetes, there is not enough scientific evidence to support the use of fenugreek for treating any health condition.

Side Effects and Cautions

  • Possible side effects of fenugreek when taken by mouth include gas, bloating, and diarrhea. Fenugreek can cause irritation when applied to the skin.
  • Given its historical use for inducing childbirth, women should use caution when taking fenugreek during pregnancy.

4. Echinacea

Echinacea has traditionally been used for colds, flu, and other infections, based on the idea that it might stimulate the immune system to more effectively fight infection. Less common folk or traditional uses of echinacea include for wounds and skin problems, such as acne or boils. Echinacea products vary widely, containing different echinacea species, plant parts, and preparations.

Strength of Evidence

  • Much research has been conducted on echinacea for the common cold. The many clinical trials of echinacea for colds have varied widely, in terms of products studied, research methods, and study results.

Study Results

  • Overall, the scientific evidence on echinacea for colds is inconclusive. There is limited evidence from some studies that some echinacea preparations might reduce the length or severity of colds in adults, but results from four NCCAM-funded clinical trials of echinacea for colds all indicated that echinacea did not reduce the length or severity of cold symptoms.
  • Echinacea has not been shown to reduce the number of colds that adults catch.
  • The effects of echinacea in children are uncertain; only a small amount of research has been done in children, and the results of that research are inconsistent.

Side Effects and Cautions

  • Few side effects have been reported in clinical trials of echinacea; however, some people may have allergic reactions.
  • In one large clinical trial in children, those who took echinacea had an increased risk of developing rashes.

5. Aloe Vera

The aloe vera plant has been a source of many folk or traditional remedies and more modern medicinal and cosmetic products. At various times aloe has been used in topical treatments to heal wounds, and to treat burns, sunburns, and psoriasis. Today aloe vera gel can be found in hundreds of skin products, including lotions and sun blocks.

Juice from the aloe plant taken orally has been used in folk or traditional remedies for a variety of conditions, including diabetes, asthma, epilepsy, and osteoarthritis.

Aloe has also been used orally as a laxative. Aloe latex contains strong laxative compounds. Products made with various components of aloe (aloin, aloe-emodin, and barbaloin) were at one time regulated by the FDA as oral over-the-counter (OTC) laxatives. In 2002, the FDA required that all OTC aloe laxative products be removed from the U.S. market or reformulated because the companies that manufactured them did not provide the necessary safety data.

The Food and Drug Administration (FDA) has approved aloe vera as a natural food flavoring.

Strength of Evidence

  • Only a few small exploratory studies have been conducted on aloe vera gel for wound healing, and for treating burns or abrasions.

Study Results

  • The results of these studies suggest that topical aloe gel may help heal burns and abrasions. One study, however, suggested that aloe gel inhibits healing of deep surgical wounds. Aloe gel has not been shown to prevent burns from radiation therapy.
  • There is not enough scientific evidence to support aloe vera for any of its many other uses.

Side Effects and Cautions

Topical Aloe Vera

  • Use of topical aloe vera is not associated with significant side effects.

Oral Aloe Vera

  • A 2-year National Toxicology Program (NTP) study on oral consumption of non-decolorized whole leaf extract of aloe vera found clear evidence of carcinogenic activity (colon tumors) in male and female rats. Whether this finding is of relevance to humans has yet to be determined, but it raises concerns about use of oral products containing aloe vera.
  • Abdominal cramps and diarrhea have been reported with oral use of aloe vera.
  • Diarrhea, caused by the laxative effect of oral aloe vera, can decrease the absorption of many drugs.
  • People with diabetes who use glucose-lowering medication should be cautious if also taking aloe by mouth because preliminary studies suggest aloe may lower blood glucose levels.
  • There have been a few case reports of acute hepatitis following oral aloe vera use but a causal relationship has not been established.

NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.

The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH's Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH Web site at NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.


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This page last modified January 16, 2013